[1] Field of the Invention
The present invention relates to a vacuum valve to be attached to a vacuum chamber of a semiconductor manufacturing apparatus, for opening and closing an aperture communicating with the vacuum chamber.
[2] Description of the Related Art
In semiconductor manufacturing apparatuses, a vacuum valve is employed for opening and closing an aperture communicating with a vacuum chamber. The vacuum valve includes a valve housing having the aperture, a valve element accommodated therein, a shaft having an end portion connected to the valve element, and a valve element driving unit that drives the shaft thereby causing the valve element to open and close the aperture.
In the vacuum valve, substances generated from a reaction are deposited onto a portion exposed to a reaction gas thereby affecting the opening and closing action of the valve element, and hence it is essential to prevent deposition of such substances. For this purpose, conventionally, a heater has been attached to the portion exposed to the reaction gas, such as the valve element and the shaft, to heat the valve, particularly the valve element, as described in Patent document, Japanese Unexamined Patent Application Publication No. 9-269072, and Patent document, Japanese Unexamined Patent Application Publication No. 11-325313.
Regarding the heating methods disclosed in Patent Literature 1 and Patent Literature 2, however, such a method as providing a heater inside the shaft and a hot plate at the back of the valve element, thereby transmitting the heat of the heater to the valve element through the hot plate, is an indirect heating method with the intermediation of the hot plate, and hence has a drawback that sufficient heat transfer efficiency cannot be attained. Another method is forming a loop-shaped groove in the back of the valve element along a periphery thereof, and placing a heater in the groove thereby heating the valve element, however the formation of the loop-shaped groove in the valve element is a troublesome work, and besides a seal plate and the hot plate have to be attached to the back of the valve element to tightly seal the groove, and therefore the attachment mechanism of the heater becomes so complicated that the heater cannot be replaced.